Brendan Gregg > Net-TcpDumpLog-0.11 > Net::TcpDumpLog



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Module Version: 0.11   Source  


Net::TcpDumpLog - Read tcpdump/libpcap network packet logs. Perl implementation (not an interface).


use Net::TcpDumpLog;

$log = Net::TcpDumpLog->new(); $log->read("/tmp/out01");

@Indexes = $log->indexes;

foreach $index (@Indexes) { ($length_orig,$length_incl,$drops,$secs,$msecs) = $log->header($index); $data = $log->data($index);

     # your code here


This module can read the data and headers from tcpdump logs (these use the libpcap log format).


new ()

Constructor, return a TcpDumpLog object.

new (BITS)

This optional argument is to force reading timestamps of that number of bits. eg new(32). Could be needed when processing tcpdumps from one OS on another.


This second options argument is how many bytes to skip for every record header. "SuSE linux 6.3" style logs need this set to 4, everything else (so far) is 0.


Read the tcpdump file indicated into memory.

indexes ()

Return an array of index numbers for the packets loaded from the tcpdump file. The indexes start at 0.

maxindex ()

Return the number of the last index. More memory efficient than indexes(). Add 1 to get the packet count. The indexes start at 0.

header (INDEX)

Takes an integer index number and returns the packet header. This is: Length of original packet, Length actually included in the tcpdump log, Number of bytes dropped in this packet, Packet arrival time as seconds since Jan 1st 1970, Microseconds

data (INDEX)

Takes an integer index number and returns the raw packet data. (This is usually Ethernet/IP/TCP data).

version ()

Returns a string containing the libpcap log version, major and minor number - which is expected to be "2.4".

linktype ()

Returns a strings containing the numeric linktype.

zoneoffset ()

Returns the zoneoffset for the packet log.

accuracy ()

Returns a the accuracy of the packet log.

dumplength ()

Returns the length of the packet log.


   perl Makefile.PL
   make test
   make install




Once you can read the raw packet data, the next step is read through the protocol stack. An Ethernet/802.3 example is,

($ether_dest,$ether_src,$ether_type,$ether_data) = unpack('H12H12H4a*',$data);

Keep an eye on CPAN for Ethernet, IP and TCP modules.


This reads tcpdump/libpcap version 2.4 logs (the most common). There could be new versions in the future, at which point this module will need updating.


If this module is not reading your logs correctly, try forcing the timestamp bits to either 32 or 64, eg "$log = Net::TcpDumpLog->new(32);". Also try printing out the log version using version() and checking it is "2.4".

There is a certain tcpdump log format "SuSE linux 6.3" that put extra fields in the log without any clear identifier. If you think you have this log, put a "4" as a second argument to new, eg "$log = Net::TcpDumpLog->new(32,4);". (The 4 specifies how many extra header bytes to skip).


Future versions should include the ability to write as well as read tcpdump logs. Also a memory efficient technique to process very large tcpdump logs (where the log size is greater than available virtual memory).



Copyright (c) 2003 Brendan Gregg. All rights reserved. This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself


Brendan Gregg <> [Sydney, Australia]

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